PITTSBURGH—Alcoa Inc. swung to a slim profit, despite lower sales and weak aluminum prices, kicking off the quarterly earnings season as it has done for decades, although for the first time not as a member of the Dow Jones Industrial Average.

Alcoa posted a net profit of $24 million, or two cents a share, largely as a result of cost-cutting efforts in its smelting operation and gains in specialty products, compared with a loss of...